Microbiological aspects of dewatering sewage sludge by removing extracellular polymeric substances during the bioleaching process: a review

Abstract

Conventional sewage treatment plants aim to minimize environmental impacts, but generate by-products, such as sludge, which also must be properly treated and dewatered. From the resource recovery perspective, a promising alternative is a reuse as fertilizer in agriculture, due to the nutrients in its composition, but the feasibility of this reuse depends on sludge treatment technologies that, in addition to promoting dewatering, treat toxic pollutants, pathogens and metals. Many techniques have been employed in an attempt to promote effective dewatering and remove pollutants from sludge, but the high cost of physicochemical treatments and risk of causing secondary pollution, make it difficult to apply on a larger scale, as well as reuse the sludge. Therefore, biological treatments, such as bioleaching, have become an increasingly popular choice, as they have economic and environmental benefits, which with improvements can enable the use of sludge as a resource. The objective of the present study was to investigate the scientific production of the last twelve years, regarding the microbiology of extracellular polymeric substances influence on sewage sludge dewatering during the bioleaching process. The specific objectives were to elucidate the influence of extracellular polymeric substances fractions on sludge dewatering, to identify the main microorganisms involved in extracellular polymeric substances generation and identify the main microorganisms involved in its removal during bioleaching. This literature review will help to understand the microbiological aspects of dewatering during the bioleaching process and will provide useful information to improve future research on the application of bioleaching in sewage sludge treatment.